For aesthetic considerations or therapeutic reasons the missing teeth in a seriously diseased set of teeth of a patient often have to be replaced by prostheses. The most commonly used prostheses are still tooth-supported or gum-supported prostheses, although the emplacement of prostheses anchored and fixed in the mandible or the maxilla of the patient by means of one or more implants screwed into holes drilled in the bone tissue, or simply inserted into osteotomies, is being developed.
Endo-osseous dental implants are divided into various categories according to their shapes and methods of insertion.
A first category consists of axial implants, or more generally of implants involving vertical insertion on the alveolar ridge. The most commonly used system of screw-in axial implants is the so-called “Branemark” system named after its inventor, who disclosed this system in France in Application FR 2,032,287 published on 27 Nov. 1970.
A second category consists of implants inserted laterally into the jawbones. These implants generally include a vertical shank intended to support the prosthesis and a seating perpendicular to the shank, consisting of a plate or one or more discs. For example, an implant of this type comprising a perforated rectangular plate is described in French Patent Application FR 2,302,715 published on 1 Oct. 1976 in the names of B. Clunet-Coste and J. Maneuf.
French Patent Application FR 2,561,907 published on 4 Oct. 1985 in the name of G. Scortecci discloses a lateral insertion implant the seating of which alternatively consists of a disc.
This second type of implants has numerous advantages over the first type, particularly when the bone volume available for the implantation is reduced, or when the opening of the buccal cavity is too small to permit an axial implant. A major advantage is the possibility of an immediate loading of the implant by the prosthesis.
However, in order to achieve this object, the osteotomy of complementary shape to the implant must be made with a very high degree of precision so as to avoid any play that could subsequently lead to a rejection phenomenon.
German Patent Application No. DE 4,026,011 published on 20 Feb. 1992 in the name of G. Lakos describes a process and a device enabling the dental surgeon's movements to be guided. This device consists of an adjustable abutment or lug fixed on the one hand to the drill turbine and resting on the other hand on the osseous ridge. In this way the milling cutter wheel is positioned at the desired height and its lateral penetration into the bone is restricted.
In the case of axial implants it is known to employ modern medical imaging techniques combined with robotic techniques so as to simulate in three dimensions on a computer the positioning of this type of implants before any surgical intervention, and to make a drilling template that will guide the dental surgeon during the operation. The implementation of these techniques has significantly increased the chance of obtaining good aesthetic results, while reducing the risk of post-operation complications.
A process and a device of this type for determining the ideal emplacement of an axial implant, and designed for the precise positioning of the latter, are described in U.S. Pat. No. 5,320,529, in the name of D. Pompa, published on 14 Jun. 1994. According to this procedure a stereolithographic model of the jawbone is produced from tomographic sections, and enables the dental surgeon to simulate on this model the positioning of the prostheses. A surgical guide is made by molding a model of the bone and radio-opaque models of the implants in situ, provided with their implant supports. Drilling barrels of interior diameters corresponding to drill bits of different sizes are then placed in the casts or impressions of the implant carriers.
The drilling template described in the International Application WO 99/26540 in the name of M. Klein et al. published on 3 Jun. 1999, adopts the above principle of using drilling barrels of different diameters inserted into bores of a single diameter, virtually the only difference being that these are inserted into cylinders that are themselves placed in bores drilled directly in the scannographic guide by a digitally controlled drilling machine starting from scanner data.
The process for making models of parts of the human body from digital images disclosed by Materialise N.V. in Belgian Patent BE 1,008,372 published on 2 Apr. 1996, and applied in particular to computer-aided implantology, avoids the molding stage by allowing not only the models of the mandible and maxilla, but also the dimensionally accurate surgical guides corresponding to any required implant plan, to be produced directly by stereolithography.
Starting from the scanner data, the implantologist prepares a virtual implant plan by means of software designed for implementing the above process, and sends the results to a dental laboratory responsible for converting these data into actual drilling templates. During the course of the operation, a template is positioned on the alveolar crest; thanks to the complex shapes of the jawbones and teeth, the positioning of the template is unique and stable. The templates contain implantable stainless steel cylinders that form physical guides for the drills during surgery and enable the drilling axes to be controlled in an optimum manner. Several templates are produced with cylinders of different diameters, enabling the drilling sequence specific to each implant to be taken into account and allowing the dental surgeon to adapt to the circumstances of each individual case. When the site is ready, the implants are inserted in the normal way by means of the implant carrier.
It thus follows from the documents cited above that various computer-aided implantology systems for the emplacement of axial implants are known from the prior art.
However, none of these systems permits the use of lateral insertion implants. Moreover, neither does there exist any surgical guide capable of realizing osteotomies specific to this particular type of implants, nor is there any process for inserting the latter in situ using such a guide.